
/* Copyright 1998, 2011, 2013 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "ares_setup.h"

#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
#include <arpa/nameser.h>
#else
#include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif

#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif

#include "ares.h"
#include "ares_inet_net_pton.h"
#include "bitncmp.h"
#include "ares_platform.h"
#include "ares_nowarn.h"
#include "ares_private.h"

#ifdef WATT32
#undef WIN32
#endif

struct host_query {
    /* Arguments passed to ares_gethostbyname() */
    ares_channel channel;
    char* name;
    ares_host_callback callback;
    void* arg;
    int sent_family; /* this family is what was is being used */
    int want_family; /* this family is what is asked for in the API */
    const char* remaining_lookups;
    int timeouts;
};

static void next_lookup(struct host_query* hquery, int status_code);
static void host_callback(void* arg, int status, int timeouts,
    unsigned char* abuf, int alen);
static void end_hquery(struct host_query* hquery, int status,
    struct hostent* host);
static int fake_hostent(const char* name, int family,
    ares_host_callback callback, void* arg);
static int file_lookup(const char* name, int family, struct hostent** host);
static void sort_addresses(struct hostent* host,
    const struct apattern* sortlist, int nsort);
static void sort6_addresses(struct hostent* host,
    const struct apattern* sortlist, int nsort);
static int get_address_index(const struct in_addr* addr,
    const struct apattern* sortlist, int nsort);
static int get6_address_index(const struct ares_in6_addr* addr,
    const struct apattern* sortlist, int nsort);

void ares_gethostbyname(ares_channel channel, const char* name, int family,
    ares_host_callback callback, void* arg)
{
    struct host_query* hquery;

    /* Right now we only know how to look up Internet addresses - and unspec
     means try both basically. */
    switch (family) {
    case AF_INET:
    case AF_INET6:
    case AF_UNSPEC:
        break;
    default:
        callback(arg, ARES_ENOTIMP, 0, NULL);
        return;
    }

    if (fake_hostent(name, family, callback, arg))
        return;

    /* Allocate and fill in the host query structure. */
    hquery = ares_malloc(sizeof(struct host_query));
    if (!hquery) {
        callback(arg, ARES_ENOMEM, 0, NULL);
        return;
    }
    hquery->channel = channel;
    hquery->name = ares_strdup(name);
    hquery->want_family = family;
    hquery->sent_family = -1; /* nothing is sent yet */
    if (!hquery->name) {
        ares_free(hquery);
        callback(arg, ARES_ENOMEM, 0, NULL);
        return;
    }
    hquery->callback = callback;
    hquery->arg = arg;
    hquery->remaining_lookups = channel->lookups;
    hquery->timeouts = 0;

    /* Start performing lookups according to channel->lookups. */
    next_lookup(hquery, ARES_ECONNREFUSED /* initial error code */);
}

static void next_lookup(struct host_query* hquery, int status_code)
{
    const char* p;
    struct hostent* host;
    int status = status_code;

    for (p = hquery->remaining_lookups; *p; p++) {
        switch (*p) {
        case 'b':
            /* DNS lookup */
            hquery->remaining_lookups = p + 1;
            if ((hquery->want_family == AF_INET6) || (hquery->want_family == AF_UNSPEC)) {
                /* if inet6 or unspec, start out with AAAA */
                hquery->sent_family = AF_INET6;
                ares_search(hquery->channel, hquery->name, C_IN, T_AAAA,
                    host_callback, hquery);
            } else {
                hquery->sent_family = AF_INET;
                ares_search(hquery->channel, hquery->name, C_IN, T_A,
                    host_callback, hquery);
            }
            return;

        case 'f':
            /* Host file lookup */
            status = file_lookup(hquery->name, hquery->want_family, &host);

            /* this status check below previously checked for !ARES_ENOTFOUND,
             but we should not assume that this single error code is the one
             that can occur, as that is in fact no longer the case */
            if (status == ARES_SUCCESS) {
                end_hquery(hquery, status, host);
                return;
            }
            status = status_code; /* Use original status code */
            break;
        }
    }
    end_hquery(hquery, status, NULL);
}

static void host_callback(void* arg, int status, int timeouts,
    unsigned char* abuf, int alen)
{
    struct host_query* hquery = (struct host_query*)arg;
    ares_channel channel = hquery->channel;
    struct hostent* host = NULL;

    hquery->timeouts += timeouts;
    if (status == ARES_SUCCESS) {
        if (hquery->sent_family == AF_INET) {
            status = ares_parse_a_reply(abuf, alen, &host, NULL, NULL);
            if (host && channel->nsort)
                sort_addresses(host, channel->sortlist, channel->nsort);
        } else if (hquery->sent_family == AF_INET6) {
            status = ares_parse_aaaa_reply(abuf, alen, &host, NULL, NULL);
            if ((status == ARES_ENODATA || status == ARES_EBADRESP || (status == ARES_SUCCESS && host && host->h_addr_list[0] == NULL)) && hquery->want_family == AF_UNSPEC) {
                /* The query returned something but either there were no AAAA
               records (e.g. just CNAME) or the response was malformed.  Try
               looking up A instead. */
                if (host)
                    ares_free_hostent(host);
                hquery->sent_family = AF_INET;
                ares_search(hquery->channel, hquery->name, C_IN, T_A,
                    host_callback, hquery);
                return;
            }
            if (host && channel->nsort)
                sort6_addresses(host, channel->sortlist, channel->nsort);
        }
        end_hquery(hquery, status, host);
    } else if ((status == ARES_ENODATA || status == ARES_EBADRESP || status == ARES_ETIMEOUT) && (hquery->sent_family == AF_INET6 && hquery->want_family == AF_UNSPEC)) {
        /* The AAAA query yielded no useful result.  Now look up an A instead. */
        hquery->sent_family = AF_INET;
        ares_search(hquery->channel, hquery->name, C_IN, T_A, host_callback,
            hquery);
    } else if (status == ARES_EDESTRUCTION)
        end_hquery(hquery, status, NULL);
    else
        next_lookup(hquery, status);
}

static void end_hquery(struct host_query* hquery, int status,
    struct hostent* host)
{
    hquery->callback(hquery->arg, status, hquery->timeouts, host);
    if (host)
        ares_free_hostent(host);
    ares_free(hquery->name);
    ares_free(hquery);
}

/* If the name looks like an IP address, fake up a host entry, end the
 * query immediately, and return true.  Otherwise return false.
 */
static int fake_hostent(const char* name, int family,
    ares_host_callback callback, void* arg)
{
    struct hostent hostent;
    char* aliases[1] = { NULL };
    char* addrs[2];
    int result = 0;
    struct in_addr in;
    struct ares_in6_addr in6;

    if (family == AF_INET || family == AF_INET6) {
        /* It only looks like an IP address if it's all numbers and dots. */
        int numdots = 0, valid = 1;
        const char* p;
        for (p = name; *p; p++) {
            if (!ISDIGIT(*p) && *p != '.') {
                valid = 0;
                break;
            } else if (*p == '.') {
                numdots++;
            }
        }

        /* if we don't have 3 dots, it is illegal
       * (although inet_addr doesn't think so).
       */
        if (numdots != 3 || !valid)
            result = 0;
        else
            result = ((in.s_addr = inet_addr(name)) == INADDR_NONE ? 0 : 1);

        if (result)
            family = AF_INET;
    }
    if (family == AF_INET6)
        result = (ares_inet_pton(AF_INET6, name, &in6) < 1 ? 0 : 1);

    if (!result)
        return 0;

    if (family == AF_INET) {
        hostent.h_length = (int)sizeof(struct in_addr);
        addrs[0] = (char*)&in;
    } else if (family == AF_INET6) {
        hostent.h_length = (int)sizeof(struct ares_in6_addr);
        addrs[0] = (char*)&in6;
    }
    /* Duplicate the name, to avoid a constness violation. */
    hostent.h_name = ares_strdup(name);
    if (!hostent.h_name) {
        callback(arg, ARES_ENOMEM, 0, NULL);
        return 1;
    }

    /* Fill in the rest of the host structure and terminate the query. */
    addrs[1] = NULL;
    hostent.h_aliases = aliases;
    hostent.h_addrtype = aresx_sitoss(family);
    hostent.h_addr_list = addrs;
    callback(arg, ARES_SUCCESS, 0, &hostent);

    ares_free((char*)(hostent.h_name));
    return 1;
}

/* This is an API method */
int ares_gethostbyname_file(ares_channel channel, const char* name,
    int family, struct hostent** host)
{
    int result;

    /* We only take the channel to ensure that ares_init() been called. */
    if (channel == NULL) {
        /* Anything will do, really.  This seems fine, and is consistent with
         other error cases. */
        *host = NULL;
        return ARES_ENOTFOUND;
    }

    /* Just chain to the internal implementation we use here; it's exactly
   * what we want.
   */
    result = file_lookup(name, family, host);
    if (result != ARES_SUCCESS) {
        /* We guarantee a NULL hostent on failure. */
        *host = NULL;
    }
    return result;
}

static int file_lookup(const char* name, int family, struct hostent** host)
{
    FILE* fp;
    char** alias;
    int status;
    int error;

#ifdef WIN32
    char PATH_HOSTS[MAX_PATH];
    win_platform platform;

    PATH_HOSTS[0] = '\0';

    platform = ares__getplatform();

    if (platform == WIN_NT) {
        char tmp[MAX_PATH];
        HKEY hkeyHosts;

        if (RegOpenKeyExA(HKEY_LOCAL_MACHINE, WIN_NS_NT_KEY, 0, KEY_READ,
                &hkeyHosts)
            == ERROR_SUCCESS) {
            DWORD dwLength = MAX_PATH;
            RegQueryValueExA(hkeyHosts, DATABASEPATH, NULL, NULL, (LPBYTE)tmp,
                &dwLength);
            ExpandEnvironmentStringsA(tmp, PATH_HOSTS, MAX_PATH);
            RegCloseKey(hkeyHosts);
        }
    } else if (platform == WIN_9X)
        GetWindowsDirectoryA(PATH_HOSTS, MAX_PATH);
    else
        return ARES_ENOTFOUND;

    strcat(PATH_HOSTS, WIN_PATH_HOSTS);

#elif defined(WATT32)
    extern const char* _w32_GetHostsFile(void);
    const char* PATH_HOSTS = _w32_GetHostsFile();

    if (!PATH_HOSTS)
        return ARES_ENOTFOUND;
#endif

    fp = fopen(PATH_HOSTS, "r");
    if (!fp) {
        error = ERRNO;
        switch (error) {
        case ENOENT:
        case ESRCH:
            return ARES_ENOTFOUND;
        default:
            DEBUGF(fprintf(stderr, "fopen() failed with error: %d %s\n",
                error, strerror(error)));
            DEBUGF(fprintf(stderr, "Error opening file: %s\n",
                PATH_HOSTS));
            *host = NULL;
            return ARES_EFILE;
        }
    }
    while ((status = ares__get_hostent(fp, family, host)) == ARES_SUCCESS) {
        if (strcasecmp((*host)->h_name, name) == 0)
            break;
        for (alias = (*host)->h_aliases; *alias; alias++) {
            if (strcasecmp(*alias, name) == 0)
                break;
        }
        if (*alias)
            break;
        ares_free_hostent(*host);
    }
    fclose(fp);
    if (status == ARES_EOF)
        status = ARES_ENOTFOUND;
    if (status != ARES_SUCCESS)
        *host = NULL;
    return status;
}

static void sort_addresses(struct hostent* host,
    const struct apattern* sortlist, int nsort)
{
    struct in_addr a1, a2;
    int i1, i2, ind1, ind2;

    /* This is a simple insertion sort, not optimized at all.  i1 walks
   * through the address list, with the loop invariant that everything
   * to the left of i1 is sorted.  In the loop body, the value at i1 is moved
   * back through the list (via i2) until it is in sorted order.
   */
    for (i1 = 0; host->h_addr_list[i1]; i1++) {
        memcpy(&a1, host->h_addr_list[i1], sizeof(struct in_addr));
        ind1 = get_address_index(&a1, sortlist, nsort);
        for (i2 = i1 - 1; i2 >= 0; i2--) {
            memcpy(&a2, host->h_addr_list[i2], sizeof(struct in_addr));
            ind2 = get_address_index(&a2, sortlist, nsort);
            if (ind2 <= ind1)
                break;
            memcpy(host->h_addr_list[i2 + 1], &a2, sizeof(struct in_addr));
        }
        memcpy(host->h_addr_list[i2 + 1], &a1, sizeof(struct in_addr));
    }
}

/* Find the first entry in sortlist which matches addr.  Return nsort
 * if none of them match.
 */
static int get_address_index(const struct in_addr* addr,
    const struct apattern* sortlist,
    int nsort)
{
    int i;

    for (i = 0; i < nsort; i++) {
        if (sortlist[i].family != AF_INET)
            continue;
        if (sortlist[i].type == PATTERN_MASK) {
            if ((addr->s_addr & sortlist[i].mask.addr4.s_addr)
                == sortlist[i].addrV4.s_addr)
                break;
        } else {
            if (!ares__bitncmp(&addr->s_addr, &sortlist[i].addrV4.s_addr,
                    sortlist[i].mask.bits))
                break;
        }
    }
    return i;
}

static void sort6_addresses(struct hostent* host,
    const struct apattern* sortlist, int nsort)
{
    struct ares_in6_addr a1, a2;
    int i1, i2, ind1, ind2;

    /* This is a simple insertion sort, not optimized at all.  i1 walks
   * through the address list, with the loop invariant that everything
   * to the left of i1 is sorted.  In the loop body, the value at i1 is moved
   * back through the list (via i2) until it is in sorted order.
   */
    for (i1 = 0; host->h_addr_list[i1]; i1++) {
        memcpy(&a1, host->h_addr_list[i1], sizeof(struct ares_in6_addr));
        ind1 = get6_address_index(&a1, sortlist, nsort);
        for (i2 = i1 - 1; i2 >= 0; i2--) {
            memcpy(&a2, host->h_addr_list[i2], sizeof(struct ares_in6_addr));
            ind2 = get6_address_index(&a2, sortlist, nsort);
            if (ind2 <= ind1)
                break;
            memcpy(host->h_addr_list[i2 + 1], &a2, sizeof(struct ares_in6_addr));
        }
        memcpy(host->h_addr_list[i2 + 1], &a1, sizeof(struct ares_in6_addr));
    }
}

/* Find the first entry in sortlist which matches addr.  Return nsort
 * if none of them match.
 */
static int get6_address_index(const struct ares_in6_addr* addr,
    const struct apattern* sortlist,
    int nsort)
{
    int i;

    for (i = 0; i < nsort; i++) {
        if (sortlist[i].family != AF_INET6)
            continue;
        if (!ares__bitncmp(addr, &sortlist[i].addrV6, sortlist[i].mask.bits))
            break;
    }
    return i;
}
